And therefore not in my stories either.

We all know (probably) by now that O'Ryan curses in rot13, not necessarily because he's always done so, but because he had been in the PPC longer than Agent!Kittyauthor. As for the others, their home canon affects how they curse:

• Kitty has been known to refer to Whitney in place of God ("Oh, in Whitney's name!") when stressed in, at least, my mind. This is because Whitney is the only other person/Mii that she knew before the PPC. Whitney was the captured queen she was supposed to rescue, but, of course, the DS was reset before that happened, and Kittyauthor landed in the PPC.
• David Null isn't exactly fond of some rules of society, and "don't curse all the time" is one of them. He curses a lot, very plainly. Back in his home canon, he was the kid that had a potty mouth because his parents had a potty mouth. When he got to the high school (for teaching, not as a kid), his mentor pointed out that not everyone was like David; not everyone knew a whole bunch of curse words by their first year of high school. David, as a new teacher, held back on the curse words until he got a better scope of the class years. Freshmen, shiny and new, rarely cursed. Sophhmores cursed, but they were told "stop" whenever they did. Juniors seemed to curse the most, and teachers were divided on whether to punish them or not. Seniors cursed less than juniors, but, with the exception of one teacher, no one really cared. David Null adapted to that the next year. He never cursed in front of his sophmores, but he cursed freely in front of his seniors because they could handle it. He still somewhat abides by that today: if a teen of unknown age approaches him, he'll restrain on his cursing. Except Sues in fanfic, he'll curse freely around them, and he'll curse freely in badfic no matter what. He also refers to "his" God as God despite not believing in one.
• K is... a person, sure. He is much kinder in teaching methods than David Null, but he is extremely harsh on curse words from his students. Likewise, he rarely curses himself. If he curses, one of two things happened. One, he is describing a movie he really liked, or two, something really bad happened. He was a devout church-goer until... two years before he became a vampire, I think? A lot of his language is, thusly, not a lot of "oh my God!" but, rather, "Lord." "Oh my Lord" is a lot more common from him than "oh my God," although the latter still happens
• Matthew, once I get around to it, curses in reference to Big Brother, which makes sense, considering his home canon and his lack of devolopment. "Oh, Big Brother in Hell!" is considered very strong for him, even though he's never been around those posters. He was a horror writer written very poorly. "Oh my gosh!" is common from Matt.
• Paye... doesn't really have a God besides "The Player," but he abandoned her, so she doesn't refer to a God.
• Crow Ressa just copies O'Ryan Keys, having come from an underdevoloped canon.

I think that's it of my characters?

-kA, still waking up.

We boarders tend to use creative curses too. I think I've invented "Fëanor on a barbecue".